The use of the bimodal production decline curve for the analysis of hydraulically fractured shale/tight gas reservoirs

The capability to conduct a rapid, near real-time model-based analysis of production data from tight/shale (TS) gas fields is important in determining fracture and matrix properties. Model-based analysis of production can range from simple analytical solutions to complex numerical models. The objective of this study is to develop a simple, Excel-based tool for the analysis of the complex problem of gas production from a fractured TS gas reservoir that is based on a robust model that is faithful to the underlying physics and can provide rapid estimates of the important system parameters. The scientifically robust model used as the basis for this tool is a significant modification and expansion of the bimodal production decline curve of Silin and Kneafsey (2012). The production period is divided into two regimes: an early-time regime before the extent of the stimulated reservoir volume (SRV) is felt, where an analytical similarity solution for gas production rate is obtained, and a late-time regime where the rate can be approximated with an exponential decline or more accurately represented with a numerical integration. Our basic model follows Silin and Kneafsey (2012) and produces the widely observed -½ slope on a log-log plot of early-time production decline curves, while our expanded model generalizes this slope to –n, where 0 < n < 1, to represent non-ideal flow geometries. The expanded model was programmed into an Excel spreadsheet to develop an interactive, user-friendly application for curve matching of well production data to the bimodal curve, from which matrix and fracture properties can be extracted. This tool allows significant insight into the model parameters that control the reservoir behavior and production: the geometry of the hydraulically-induced fracture network, its flow and transport properties, and the optimal operational parameters. This information enables informed choices about future operations, and is valuable in several different ways: (a) to estimate reserves and to predict future production, including expected ultimate recovery and the useful lifetime of the stage or the well; (b) if curve-matching is unsuccessful, to indicate the inadequacy of the mathematical model and the need for more complex numerical model to analyze the system; (c) to verify/validate numerical models, and to identify anomalous behavior or measurement errors in the data. The present approach can be adapted to gas-flow problems in dual-permeability media (hydraulically or naturally fractured) or highly heterogeneous sedimentary rock, as well as to retrograde condensation

A Production Characterization of the Eagle Ford Shale, Texas - A Bayesian Analysis Approach

We begin this research by asking "can we better estimate reserves in unconventional reservoirs using Bayes' theorem?" To attempt to answer this question, we obtained data for 68 wells in the Greater Core of the Eagle Ford Shale, Texas. As process, we eliminated the wells that did not have enough data, that did not show a production decline and/or wells that had too much data noise (this left us with 8 wells for analysis). We next performed decline curve analysis (DCA) using the Modified Hyperbolic (MH) and Power-Law Exponential (PLE) models (the two most common DCA models), consisting in user-guided analysis software. Then, the Bayesian paradigm was implemented to calibrate the same two models on the same set of wells. The primary focus of the research was the implementation of the Bayesian paradigm on the 8 well data set. We first performed a "best fit" parameter estimation using least squares optimization, which provided an optimized set of parameters for the two decline curve models. This was followed by using the Markov Chain Monte Carlo (MCMC) integration of the Bayesian posterior function for each model, which provided a full probabilistic description of its parameters. This allowed for the simulation of a number of likely realizations of the decline curves, from which first order statistics were computed to provide a confidence metric on the calibration of each model as applied to the production data of each well. Results showed variation on the calibration of the MH and PLE models. The forward models (MH and PLE) either over- or underestimate the reserves compared with the Bayesian calibrations, proving that the Bayesian paradigm was able to capture a more accurate trend of the data and thus able to determine more accurate estimates of reserves. In industry, the same decline curve models are used for unconventional wells as for conventional wells, even though we know that the same models may not apply. Based on the proposed results, we believe that Bayesian inference yields more accurate estimates of reserves for unconventional reservoirs than deterministic DCA methods. Moreover, it provides a measure of confidence on the prediction of production as as function of varying data and varying decline curve models

Simulation of Gas Production from Multilayered Hydrate-Bearing Media with Fully Coupled Flow, Thermal, Chemical and Geomechanical Processes Using TOUGH+Millstone. Part 3: Production Simulation Results

The TOUGH+Millstone simulator has been developed for the analysis of coupled flow, thermal and geomechanical processes associated with the formation and/or dissociation of CH -hydrates in geological media. It is composed of two constituent codes: (a) a significantly enhanced version of the TOUGH+Hydrate simulator, v2.0, that accounts for all known flow, physical, thermodynamic and chemical processes associated with the evolution of hydrate-bearing systems and includes the most recent physical properties relationships, coupled seamlessly with (b) Millstone v1.0, a new code that addresses the conceptual, computational and mathematical shortcomings of earlier codes used to describe the geomechanical response of these systems. The capabilities of the TOUGH+Millstone code are demonstrated in the simulation and analysis of the system flow, thermal, and geomechanical behavior during gas production from a realistic complex offshore hydrate deposit. In the third paper of this series, we apply the simulators described in parts 1 and 2 to a problem of gas production from a complex, multilayered system of hydrate-bearing sediments in an oceanic environment. We perform flow simulations of constant-pressure production via a vertical well and compare those results to a coupled flow-geomechanical simulation of the same process. The results demonstrate the importance of fully coupled geomechanics when modeling the evolution of reservoir properties during production.

Simulation of Gas Production from Multilayered Hydrate-Bearing Media with Fully Coupled Flow, Thermal, Chemical and Geomechanical Processes Using TOUGH + Millstone. Part 1: Numerical Modeling of Hydrates

TOUGH + Millstone has been developed for the analysis of coupled flow, thermal and geomechanical processes associated with the formation and/or dissociation of CH4-hydrates in geological media. It is composed of two constituent codes: (a) a significantly enhanced version of the TOUGH + HYDRATE simulator, V2.0, that accounts for all known flow, physical, thermodynamic and chemical processes associated with the behavior of hydrate-bearing systems undergoing changes and includes the most recent advances in the description of the system properties, coupled seamlessly with (b) Millstone V1.0, a new code that addresses the conceptual, computational and mathematical shortcomings of earlier codes used to describe the geomechanical response of these systems. The capabilities of TOUGH + Millstone are demonstrated in the simulation and analysis of the system flow, thermal and geomechanical behavior during gas production from a realistic complex offshore hydrate deposit. In the first paper of this series, we discuss the physics underlying the T + H hydrate simulator, the constitutive relationships describing the physical, chemical (equilibrium and kinetic) and thermal processes, the states of the CH + H O system and the sources of critically important data, as well as the mathematical approaches used for the development of the of mass and energy balance equations and their solution. Additionally, we provide verification examples of the hydrate code against numerical results from the simulation of laboratory and field experiments. 4

Effectiveness of multi-stage cooling processes in improving the CH4-hydrate saturation uniformity in sandy laboratory samples

Laboratory-created samples of methane hydrate (MH)-bearing media are a necessity because of the rarity and difficulty of obtaining naturally-occurring samples. The hypothesis that the inevitable heterogeneity in the phase saturations of the laboratory samples may lead to unreliable and non-repeatable results provided the impetus for this study, which aimed to determine the conditions under which maximum uniformity can be achieved. To that end, we designed four experiments involving different multi-stage cooling regimes (in terms of their duration and number of stages) to induce MH formation under excess-water conditions. In the absence of direct visualization capabilities, we analysed the experimental results by means of numerical simulation, which provided high-resolution predictions of the spatial distributions of the phase saturations in the cores and enabled the estimation of the parameters controlling the kinetic MH-formation behaviour through history-matching. Analysis of the numerical results indicated that, under the conditions of the experiments and with the design of the reactor, significant heterogeneities in phase saturation distributions were observed in all cases, leading to the conclusion that it is not possible to obtain cores with uniform phase saturation. Additionally, contrary to expectations, heterogeneities increased with the number of cooling stages and the duration of cooling, and this was attributed to imperfect insulation of the upper part of the reactor. A set of simulations involving perfect insulation of the reactor top confirmed the validity of this assumption: (a) predicting the formation of high-uniformity MH-bearing cores that became more homogeneous as the number of cooling stages and the length of the cooling period increased; and (b) providing important information for the improvement of the standard design of the experimental apparatus for the laboratory creation of MH-bearing cores using the excess water method

TOUGH+Hydrate v1.0 User's Manual: A Code for the Simulation of System Behavior in Hydrate-Bearing Geologic Media

TOUGH+HYDRATE v1.0 is a new code for the simulation of the behavior of hydrate-bearing geologic systems. By solving the coupled equations of mass and heat balance, TOUGH+HYDRATE can model the non-isothermal gas release, phase behavior and flow of fluids and heat under conditions typical of common natural CH{sub 4}-hydrate deposits (i.e., in the permafrost and in deep ocean sediments) in complex geological media at any scale (from laboratory to reservoir) at which Darcy's law is valid. TOUGH+HYDRATE v1.0 includes both an equilibrium and a kinetic model of hydrate formation and dissociation. The model accounts for heat and up to four mass components, i.e., water, CH{sub 4}, hydrate, and water-soluble inhibitors such as salts or alcohols. These are partitioned among four possible phases (gas phase, liquid phase, ice phase and hydrate phase). Hydrate dissociation or formation, phase changes and the corresponding thermal effects are fully described, as are the effects of inhibitors. The model can describe all possible hydrate dissociation mechanisms, i.e., depressurization, thermal stimulation, salting-out effects and inhibitor-induced effects. TOUGH+HYDRATE is the first member of TOUGH+, the successor to the TOUGH2 [Pruess et al., 1991] family of codes for multi-component, multiphase fluid and heat flow developed at the Lawrence Berkeley National Laboratory. It is written in standard FORTRAN 95, and can be run on any computational platform (workstation, PC, Macintosh) for which such compilers are available

Evaluation of alternative horizontal well designs for gas production from hydrate deposits in the Shenhu area, South China Sea

Gas hydrate deposits were confirmed in the Shenhu Area, the north slope of South China Sea during a drilling expedition in 2007. Hydrate deposits in the area are distributed in disseminated forms in forams-rich clay sediments with permeable overburden and underburden layers. Production of gas from such a type of hydrate deposits is very challenging. In this study, we develop a numerical approach for investigation of gas production strategies by horizontal wells and preliminary estimation of the production potential based on the limited data that are currently available. Numerical models are built to represent the typical hydrate deposits in the area, including the thickness of the Hydrate-Bearing Layer (HBL), hydrate saturation, water depth, temperature at the sea floor, initial thermal gradient and pressure distribution. The models are used to simulate the different production schemes and well designs. In this paper, production strategies of horizontal well system with combination of depressurization and thermal stimulation are investigated through numerical models. Gas production potential from the deposits and effectiveness of the different production methods are evaluated. The simulation results indicate that with current technology, gas production from Shenhu hydrate deposits may not be economically efficient for all the production strategies we have investigated. Copyright 2010, Society of Petroleum Engineers

Reserves and Resources Tracking

In this work, we develop a robust methodology for hydrocarbon inventory management by creating visual representations describing how volumes move from Prospective Resources to Reserves. This helps engineers visualize how volumes move for a given project, and also provides a visual description of the definitions in the Petroleum Resources Management System (PRMS) document, which is dense and can be difficult to understand. We propose methods to understand and quantify expected Reserves and Resources other than Reserves (ROTR) assets at any future time, incorporating the uncertainties that cause a change between the different Reserves and ROTR categories. We also develop a methodology to simulate the progression of hydrocarbons through the value chain based on actual events or specific planning strategies. The model will work in resources volumes, but we will incorporate conversions allowing us to quantify these volumes in units of energy or mass. The results from the proposed model are acceptable for decision making, can reduce analysis time, and may reduce the need for traditional evaluation methods. Furthermore, we incorporate the chance of commerciality (COC) to show the impact through the development of a project. This is a novel approach that shows the mathematical impact of the COC on Reserves and ROTR volumes. We then propose a methodology that aims to help engineers understand the spatial and time relationship of hydrocarbons. The results from this work show the impact of well spacing on Reserves, and discuss the time to move through different sub-classes which can be used to determine the return on investment. Finally, we discuss model accuracy through time by comparing a truncated dataset to a full dataset estimation results. Ideally, we want our initial estimates with the truncated dataset to be accurate. By comparing the amount of hydrocarbon booked as Reserves from the truncated dataset to the amount booked from the full dataset, we see the accuracy of the model through time. We aim to increase the accuracy of earlytime estimates to reduce the need to re-run the model, and to have a better understanding of the actual Reserves for the future of the project

Finger tracking and hand recognition technologies in virtual reality maritime safety training applications

The competitiveness and development of the maritime sector together with the continuous effort on increasing operations performance while reducing operations costs, drives the needs for on-board effective and qualitative training safety related issues. Virtual reality (VR) has been considered by classification societies and training organizations as a technology that can significantly improve seafarer's performance and competence with the adaptation of maritime applications developed for design simulation and gaming. This paper presents the evolution of the MarSEVR (Maritime Safety Education with VR) technology as a new concept and technology by integrating finger tracking and hand recognition technologies that increase immersiveness and user engagement within the MarISOT technology, a Green Ocean innovation composed of VR safety applications. The paper approaches this integration by addressing game design, pedagogic and cognitive neuroscience principles and challenges on the use of hand recognition and finger tracking in the MarSEVR learning episodes